A stator core constituting a stator of a rotating electrical machine is constructed, for example, by stacking a number of annular iron core materials. The iron core material has an outer circumference formed with a plurality of lugs protruding radially outward from the outer circumference. The lugs are formed with respective holes. Connecting members are inserted into the holes to interconnect the iron core materials in a stacking direction.
In a conventional stator core, for example, a band-shaped magnetic steel sheet is punched out by a press thereby to be formed into the iron core material. In this case, a band-shaped magnetic steel sheet has portions which are to be punched out by the press and are arranged into a plurality of rows along a lengthwise direction of the sheet.
When an iron core material having lugs is manufactured, a large amount of material tends to remain around a part of a magnetic steel sheet corresponding to a lug of the iron core material to be punched out. As a result, improving the yield of material has been required.